Irrigation, erosion control, root growth control and clean-up techniques

ABSTRACT

The invention provides processes for coating the surface of substrates such as a sheet, film, foam, fiber, etc., with a curable liquid resin or solution of curable resin, then in one embodiment, stably attaching a superabsorbent polymeric powder to such resin, and then curing the resin to form a coated superabsorbent product. Such substrates may include polymeric materials. Other process embodiments utilizing curable and thermoplastic resinous powders may be used instead of curable liquid resins and resulting products are included in the invention. The coated product may be utilized for water and nutrient retention in combination with irrigation, erosion control, to direct plant root growth, and to clean up standing water and petroleum spills.

[0001] This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 10/357,907 filed Feb. 4, 2003, which in turn is acontinuation-in-part of U.S. patent application Ser. No. 09/982,342filed Oct. 18, 2001. This patent application, through its parent U.S.patent application Ser. No. 09/982,342, claims priority under 35 U.S.C.119(e) from provisional application Serial No. 60/242,926 filed Oct. 25,2000 incorporated herein by reference in its entirety.

[0002] The present invention relates to highly absorbent products thatcan, for example, be interposed between liquid permeable and non-liquidpermeable sheets to form a disposable absorbent product intended for theabsorption of fluids, such as body fluids or used as a wiping sheet andprocesses of making such products. The invention may also be used as aliquid retention device and element thereof. For example, the inventionmay be utilized to absorb and retain water and nutrients contained insoil or any other growing media, thereby optimizing plant growth byminimizing loss of water and nutrients, conserving water, and/orreducing the need for future watering. The invention may also beutilized to absorb water and other aqueous media to control erosion ofsoil and the like, to control and direct plant root growth, and to cleanup petroleum spills and standing water.

BACKGROUND OF THE INVENTION

[0003] Disposable absorbent products currently find widespread use inmany applications. For example, in the infant and childcare areas,diapers and training pants have generally replaced reusable clothabsorbent articles. Other typical disposable absorbent products includefeminine care products such as sanitary napkins, panty shields, ortampons; adult incontinence products; and health care products such assurgical drapes or wound dressings. A typical disposable absorbentproduct generally comprises a composite structure including a top sheet,a back sheet, and an absorbent core structure between the top sheet andback sheet. These products usually include some type of fastening systemfor fitting the product onto the wearer.

[0004] The use of water-swellable, generally water-insoluble absorbentmaterials, commonly known as superabsorbent polymers (“SAP”), indisposable absorbent personal care products is known. Such absorbentmaterials are generally employed in absorbent products in order toincrease the absorbent capacity of such products while reducing theiroverall bulk. Such absorbent materials are generally present inabsorbent products in the form of small particles in a fibrous matrix,such as a matrix of wood pulp fluff. A matrix of wood pulp fluffgenerally has an absorbent capacity of about 6 grams of liquid per gramof fluff. The superabsorbent materials generally have an absorbentcapacity of at least about 10, preferably of about 20, and often of upto 100 times their weight in water. Clearly, incorporation of suchsuperabsorbent materials in disposable absorbent products can reduce theoverall bulk while increasing the absorbent capacity of such products.

[0005] The absorbent products mentioned above, such as baby diapers,adult incontinence devices, and feminine hygiene products, may be madewith a cellulose fiber fluff-based absorbent core sandwiched between aliquid pervious top sheet, which allows the unobstructed passage offluid to the absorbent core, and a liquid impervious backing sheetusually of plastic material, which contains the absorbed fluid andprevents it from passing through the absorbent core and soiling theundergarments or clothing of the wearer of the absorbent article.

[0006] The absorbent core of these absorbent articles may be constructedof defiberized wood pulp with or without superabsorbent polymergranules. The absorbent core may be formed on a pad-forming unit of aconverting machine on a carrier tissue to facilitate processing. Someabsorbent core forming units are equipped with layering capability inwhich a second discrete fluff layer may be laid over a primaryfluff-based absorbent layer to form a multi-layer absorbent structure.In these absorbent structures, the primary layer may include loose,superabsorbent polymer granules. It is believed that commercially usedsuperabsorbent polymer granules typically have a coarse sizedistribution. For example, Atofina reported on its website(www.aquakeep-sap.com) on Oct. 15, 2001, that its AQUAKEEP®superabsorbent polymers may be used in diapers and adult incontinenceproducts and have a particle size distribution of less than 0.5%<45microns, less than 3%>850 microns; with an average particle sizedistribution of around 420 microns. Such particle size distributioncontains a large amount of particles below 850 microns.

[0007] In recent years, market demand for thinner and more comfortableabsorbent articles has increased. Ultra-thin feminine napkins are nolonger constructed from loose wood pulp, which tends to give a bulkyproduct, but with a roll good-based air-laid absorbent cores in which aroll or coil of preformed absorbent core material is unwound directlyonto the absorbent pad-making machine without the defiberization steprequired for fluff-based products. The roll good-based approach resultsin a product thinness, which cannot be achieved by loose fluff-basedtechnology. As will be seen later, the present invention can producethinner absorbent products that have the same absorbance properties asthicker products.

[0008] U.S. Pat. No. 5,720,832, entitled “Method of Making a MeltblownNonwoven Web Containing Absorbent Particles”, describes yet anotherapproach to the field of the present invention. This patent may contactfreshly extruded microfibers with particles that may be composed ofsuperabsorbent materials. The particles are electrostatically chargedand applied to the fibers while such fibers are still tacky followingextrusion. The result of such application appears to be a physicaladherence of the powder to the wet fiber. Adherence can includeembedding the particles into the fiber surface when an embossingtechnique is used.

[0009] U.S. Pat. No. 5,419,955 involves the use of superabsorbentparticles and sheets to improve absorbency and retention properties.This technique forms a suspension of the particles to avoid problemswith powder agglomeration and powder loss.

[0010] The invention of this application avoids the need for tacky,freshly extruded fibers as a starting material in a simple,straightforward manner. Typically such freshly extruded fibers arebelieved to be sufficiently tacky to function as described inaforementioned U.S. Pat. No. 5,720,832 for less than about one minutefollowing extrusion. Thus, a very narrow processing window exists.Fibers or other materials that have been made and stored over a periodof time longer than about one minute prior to coating and powder coatingmay be utilized in this invention. Also, while the need to useparticle-containing suspensions is avoided, the objectives of avoidingpowder agglomeration and powder loss are achieved by this invention.Accordingly, the objectives of the prior art are achieved without theaccompanying constraints.

[0011] Superabsorbent polymeric particles, tablets, and emulsions havebeen used for the purposes of minimizing the loss of water and nutrientsin soils, for erosion control, in combination with irrigationprocedures, and for clean up of water and petroleum. However, none ofthese uses appear to involve adhering superabsorbent powders on asubstrate or a substrate having openings extending through thesubstrate. Solid or fibrous polymeric films, such as sheets or strips,or of any other desired shape or form such as round, cylindrical(including wrapped layered cylinders), or any other shapes, constitute asuitable substrate. The above-described uses appear to merely involvethe dispersal of superabsorbent polymeric particles in soil and othergrowing media. Erosion control is believed to employ dispersed particlesand/or perforated sheet-like barriers. Neither of these techniquesappears to involve the combination of the invention, i.e., adheredsuperabsorbent polymeric powder stably coated on a substrate.

[0012] The long-standing problem in the art of the control of plant rootgrowth has been addressed by using herbicides placed underground to haltroot growth into undesired areas such as curbs, sidewalks, roads, paths,septic fields, etc. An example of such technology may be found at thewebsite of Horticulture Alliance, Inc. athttp://www.hortsorb.com/Biobarrier.asp. The present invention solvessuch problem by a different, highly advantageous method, i.e., the rootsare attracted to desired areas and therefore growth is minimized inundesired areas. Such method is positive to the plant and itsenvironment when contrasted with the use of herbicides to kill roots atundesired locations when it is considered that herbicides are not placedand thus cannot remain in the ground.

[0013] Prior methods of water or petroleum clean up involve placingparticles of superabsorbent polymeric powder or petroleum absorbentpowder in the area of the standing water or petroleum spill, permittingabsorption of water or petroleum, and then collecting the looseparticles. On the other hand, the present invention utilizes an elementcoated with such particles, which may be removed following contact withthe water or petroleum. The above-mentioned collection process is thusavoided.

SUMMARY OF THE INVENTION

[0014] The process of the present invention involves coating the surfaceof a polymeric material, such as fiber, sheet, foam, film, etc., withcurable liquid resin compositions such as acrylates, unsaturatedpolyesters, epoxies, urethanes, acrylics, monomer-containing liquidsthat become superabsorbent when polymerized or cured, etc., applying asuperabsorbent polymeric powder to the coating, and then curing the saidcoating to cause the powder to adhere to the coated polymeric material.It is possible to form a superabsorbent polymer coating by applyingmonomer-containing liquid resins to the polymeric material surface priorto applying the superabsorbent polymeric powder and then curing theliquid resin particle coating. Curing or polymerizing the monomer willcreate the desired superabsorbent polymer coating and also adhere thesuperabsorbent particles thereto. It is also contemplated that asuperabsorbent coating, without superabsorbent polymer powders orparticles, could be utilized in absorbent materials if so desired.Curing may be effected by thermal or radiation means or a combinationthereof. UV curing offers a convenient curing process for saidmonomer-containing liquid resins.

[0015] The present invention also involves a process for stably adhering(or affixing) superabsorbent polymeric powder onto substrates, such asnatural or synthetic fibrous materials, polymeric sheets having openingsextending through the sheet, etc. One embodiment involves providing asuitable substrate, applying a superabsorbent polymeric powder to asurface of such substrate, further applying a thermoplastic resinouspowder to the substrate to form a coating thereon, and then heating thecoating to cause at least a portion of the thermoplastic resinous powderto melt and thereby cause the superabsorbent polymeric powder to becomestably adhered to the substrate. In addition, the thermoplastic resinouspowder may be applied prior to application of the superabsorbentpolymeric powder and then stably adhered by heating to cause melting ofthe thermoplastic resinous powder. Finally, a mixture of superabsorbentpolymeric powder and the thermoplastic resinous powder may be applied tothe substrate followed by heating to melt the thermoplastic resinouspowder to stably adhere the superabsorbent polymeric powder to theunderlying substrate.

[0016] The present invention also involves a process for stably adhering(or affixing) superabsorbent polymeric powder onto substrates, forexample, such as natural or synthetic polymeric fibrous materials orsheets having openings extending through the sheet. One embodimentinvolves providing a suitable substrate, applying a superabsorbentpolymeric powder to a surface of such substrate, further applying acurable resinous powder to the substrate to form a coating thereon, andthen heating the coating to cause at least a portion of the curableresinous powder to cure and thereby cause the superabsorbent polymericpowder to become stably adhered to the substrate. In addition, thecurable resinous powder may be applied prior to application of thesuperabsorbent polymeric powder and then stably adhered by heating tocause curing of the curable resinous powder. Finally, a mixture ofsuperabsorbent polymeric powder and the curable resinous powder may beapplied to the substrate followed by heating to cure the curableresinous powder to stably adhere the superabsorbent polymeric powder tothe underlying substrate.

[0017] The present invention also comprises mixtures of superabsorbentpolymeric powders and thermoplastic resinous powders for use in theabove-discussed processes. Thermoplastic resinous powders includingvinyls, polyolefins, nylons, polyesters, and copolymers such as ethyleneand vinyl alcohol may be advantageously used in the processes. Suchcopolymers melt at relatively low temperatures, such as below about 200°C. When the melted thermoplastic resinous powder contacts both thesubstrate and the superabsorbent polymeric powder, the superabsorbentpolymeric powders becomes stably adhered to the substrate.

[0018] The present invention also comprises mixtures of superabsorbentpolymeric powders and curable resinous powders for use in theabove-discussed processes. Commonly available coating powders aresuitable. Especially preferred are powders that cure by radiation orthermally at temperatures below about 400° F. As the superabsorbentpolymeric powder does not cure, such powder becomes stably adhered tocured resinous powder and thereby ultimately becomes stably adhered tothe substrate because upon curing, the curable powder becomes stablyadhered to the substrate.

[0019] It is also contemplated to provide thin films of thermoplasticresinous materials; to apply superabsorbent polymeric powders to thesurface of such films; and to heat the film to cause melting orsoftening of the film, thereby stably adhering the powders to the film.Alternatively, the superabsorbent polymeric powder may be heated priorto being applied to the film to an extent that the thin film becomesmelted or softened at the point of contact between the film and thepowder to stably adhere the powder to the thin film.

[0020] The present invention also comprises a product having a polymericmaterial with an at least partially cured resinous coating and furtherhaving a superabsorbent polymeric powder adhered to such coating to forma stable, highly absorbent product that can be used for example, as adisposable absorbent product for the absorption of fluids, includingbody fluids or as a wiping cloth.

[0021] As can be appreciated, several long-standing problems in the artare solved by the invention; namely, superabsorbent polymer particleagglomeration and loss; the need for a freshly formed fiber as astarting material (such as the extruded fibers of U.S. Pat. No.5,720,832); and the need for particle-containing suspensions (such asshown in U.S. Pat. No. 5,419,955). The particles of this invention arelocated at the surface of the coating rather than mixed within asuspension and thus, effectively disposed to contact and absorb thefluid.

[0022] More specifically, the present invention is advantageous over theabove discussed prior art because it can stably adhere particles tocoated polymeric surfaces. Such result is achieved through use of aliquid resinous coating on the polymeric surface with subsequent curingto adhere the coating to the polymeric material and to thesuperabsorbent polymeric powder particles. These techniques reduceagglomeration, powder loss, and migration of such powder through theproduct to the user's skin. Adherence of the particles offers a furtheradvantage due to improved migration of absorbed liquids or fluids fromthe superabsorbent polymer particles into the coating and polymericmaterial, thus, the overall absorbency of the absorbent product isenhanced because of stable adherence. Thus, one of the major problems inprior art products is addressed by the present invention throughincreased migration of such liquids or fluids into other portions of theabsorbent product. The invention also requires less bulk thanconventional products thereby reducing solid waste disposal space.

[0023] The absorbent products of the present invention are suited foruse in disposable products including disposable absorbent products suchas diapers, diaper liners, training pants, wraps and covers, adultincontinence products, and bed pads; incontinence devices; femininehygiene products such as sanitary napkins, panty shields, or tampons;other absorbent products such as wipes, bibs, wound dressings andsurgical capes or drapes, mattress covers and puddle pads. Accordingly,in another aspect, the present invention relates to a disposableabsorbent product utilizing the absorbent products of the presentinvention as a component.

[0024] The above-described liquid retention product also has applicationto the field of absorbent products. For example, such product could beused alone or in combination with other absorbent materials inpreviously-described absorbent products such as diapers, femininehygiene products, adult incontinence products, wiping sheets, surgicaldrapes, etc. An important aspect of using this product for absorbentproduct applications is that the size and weight of the absorbentproduct would be reduced, thereby conferring benefits of comfort andappearance to the user and also creating less solid waste per unit. Thislatter advantage is an important factor for waste disposal sites. Someabsorbent products contain an acquisition layer to absorb and then moreslowly disperse urine or other liquid into a superabsorbent polymericpowder containing portion of the absorbent product. In accordance withthis invention, the use of fine superabsorbent polymeric powder with itsattendant rapid absorption rates may reduce the size of, or eliminatethe need for, such acquisition layer.

[0025] The process and products of the present invention may also beadvantageously employed in the field of water and nutrient retention forincorporation into growing media, such as soil, and in the fields oferosion control, irrigation control, and plant root growth control. Aproduct suitable for such applications comprises water-containing liquidretention devices and elements thereof. Such elements or devices mayconveniently comprise sheets (typically polymeric and having holesextending through the sheet), cylinders or other shaped elements andcoated, on one or both sides, or at an interior surface, with asuperabsorbent polymeric powder and an at least partially meltedthermoplastic resinous powder or coated with superabsorbent polymericpowder and an at least partially cured resin.

[0026] Specifically, the present invention involves a method ofimproving water utilization efficiency, comprising placing an elementhaving superabsorbent polymeric powder stably adhered thereto at adesired location under the ground, contacting said superabsorbentpolymeric powder with water to cause said water to become absorbed intosaid superabsorbent polymeric powder, thereby storing said water in saiddesired location under the ground for future dispersion. This techniqueis especially desirable for conserving water applied by irrigationprocesses for agricultural and landscaping purposes. Lesser amounts ofwater required by future irrigation would be needed because stored waterwould be consumed following absorption and thus not be permitted toescape through the soil.

[0027] In addition, the present invention pertains to a method ofdirecting plant root growth, especially for trees, grass, and any otherplants, comprising placing an element having superabsorbent polymericpowder stably adhered thereto at a location under the ground where rootgrowth is desired to be directed, contacting said superabsorbentpolymeric powder with water, and optionally also a plant nutrient, tocause said water to become absorbed into said superabsorbent polymericpowder, thereby storing said water and nutrient, if a nutrient is added,in said desired location under the ground to cause plant roots to growtoward said desired location. In addition, a powdered or granular plantnutrient may be stably adhered to the element along with thesuperabsorbent polymeric powder.

[0028] Also, the present invention pertains to a method of reducing soilerosion, comprising placing a barrier element having superabsorbentpolymeric powder stably adhered thereto at a desired location under theground, contacting said superabsorbent polymeric powder with water tocause said water to become absorbed into said superabsorbent polymericpowder, thereby storing said water in said desired location under theground and thereby reducing soil erosion.

[0029] Finally, a method for cleaning up undesired liquids, such aswater or petroleum, disposed in an area on a surface is conducted byplacing an element having an absorbent material stably adhered theretoin such area to absorb the liquid and then removing the element from thearea to result in the removal of at least some of the liquid.

[0030] The above-described liquid retention product and absorbentproducts maybe conveniently formed into coils, cut to length, and placedinto a desired product as an absorbent core, thereby affordingsubstantial process advantages. Such advantage is especially importantfor continuous manufacturing processes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Polymeric materials may include the superabsorbent polymers setforth below or non-superabsorbent polymers such as polyurethane,polyester, polyethylene, cellulosic, polyolefin, and the like.

[0032] It is also contemplated by the invention to utilize co-extrudedfibers having a non-superabsorbent polymeric core with a superabsorbentpolymeric outer layer as a polymeric material.

[0033] Superabsorbent polymeric powders suitable for use in the presentinvention include, but are not limited to, a wide variety of anionic,cationic, and nonionic materials. Suitable polymers includepolyacrylamides, polyvinyl alcohols, ethylene maleic anhydridecopolymer, polyvinylethers, polyacrylic acids, polyvinylpyrrolidones,polyvinylmorpholines, polyamines, polyethyleneimines, polyquaternaryammoniums, natural based polysaccharide polymers such as carboxymethylcelluloses, carboxymethyl starches, hydroxypropyl celluloses, algins,alginates, carrageenans, acrylic grafted starches, acrylic graftedcelluloses, chitin, chitosan, and synthetic polypeptides such aspolyaspartic acid, polyglutamic acid, polyasparagins, polyglutamines,polylysines, and polyarginines, as well as the salts, copolymers, andmixtures of any of the foregoing polymers. Anionic polyacrylamidepolymers are an example of a suitable material.

[0034] Curable liquid resins for coating the above-mentioned polymericmaterials include acrylates, unsaturated polyesters, epoxies, urethanes,acrylics, monomer-containing liquids that become superabsorbent whenpolymerized or cured, etc. Because urethanes and superabsorbent polymersabsorb moisture, such resins can also contribute to liquid absorptionand thus further increase the total absorbency. In this regard,superabsorbent polymers are preferred to urethanes from the standpointof maximizing the overall liquid absorbency of the absorbent product.

[0035] The liquid resins can be applied or coated on the surface of thepolymeric material by conventional techniques such as misting, spraying,dipping, curtain coating, slot coating, immersion, aspiration, and thelike. Alternatively, the resin may be placed in solution, coated on thepolymeric material in liquid solution form, and the solvent thenevaporated to leave a highly concentrated coating of the resinousmaterial on the surface of the polymeric material. The balance of thesolvent will be evaporated following adherence of the superabsorbentpowder particles to the concentrated coating. Polyacrylic acid dissolvedin water is a suitable liquid coating. Other combinations of materialsand solvents are considered to be part of the invention. Water is apreferred solvent due to environmental factors, but organic solventssuch as ethanol and methanol, would also function as a solvent.Evaporation can be achieved by simply sitting at room temperature oraccelerated by a temperature increase.

[0036] As mentioned above, a liquid-containing monomer may be coatedonto the surface of a polymeric material and then cured to form asuperabsorbent polymeric coating. While the monomer is in liquid form,superabsorbent powder may be applied to the liquid coating and followedby curing of the liquid by thermal or radiation means. Electrostaticcharging of the powder prior to application is optional. Such procedurewill cure the liquid monomer-containing resin and stably adhere thepowder to the cured coating. In some instances, powder application maynot be necessary and reliance can be solely placed on the superabsorbentcoating. For example, where the polymeric material is fibrous in nature,a superabsorbent polymer coating without the need for superabsorbentpowders could be satisfactory due to the relatively large surface andthat a fiber provides as contrasted with a sheet, foam, or film whichhave lesser surface areas per unit of weight.

[0037] Superabsorbent polymeric powders or particles are applied to theliquid resin coated surface of polymeric material through contact.Advantageously, such application can be achieved by directing a streamof superabsorbent polymeric powder particles against the coatedpolymeric surface. Such streams may be airborne and, if the particledoes not readily adhere to the coating, the particles may beelectrostatically charged by corona discharge or tribocharging toimprove initial adherence prior to at least partially curing saidapplied coating. Such techniques will serve to improve transferefficiency of the powder. Another technique is to incorporate additivesinto the resinous coating composition to improve powder attraction.Surfactants, such as a sodium salt of a sulfonic acid and ammonium saltswith long aliphatic chains and the like, are suitable.

[0038] Alternatively, a superabsorbent polymeric powder could be appliedto a polymeric material surface and then such applied powder can beadhered through the application of a resinous coating and subsequentcuring. Said coating may be a liquid resin or a resinous coating powder,which transforms to a solid coating upon curing. Conventionalthermosetting or thermoplastic resinous powder coatings are suitable.Curing may be thermal or radiation. The curing temperatures and/orradiation curing procedure will cure the liquid resin or resinouscoating powder but the superabsorbent polymeric powders, unlike theresinous liquid or powders, will remain in the same solid particle statebecause such superabsorbent powders will not melt, flow or otherwisetransform during curing. This procedure would serve to contain or adherethe superabsorbent polymeric powder between the polymeric material andcoating, thereby achieving the aforesaid advantages of the presentinvention.

[0039] Another embodiment of the process mentioned in the precedingparagraph comprises applying superabsorbent polymeric powders that arecoated with a resinous material to a polymeric material and then curingthe resinous coating on such powders. Curing results in the cure of theresinous outer coating but does not alter the superabsorbent polymericpowder. Adherence to the polymeric materials is obtained throughadhesion of such cured outer coating. Such coated powders could also becontained in a mixture, emulsion, etc.

[0040] Another embodiment for adhering superabsorbent polymeric powderto a polymeric material comprises providing a mixture of asuperabsorbent polymeric powder and a resinous coating powder, applyingsuch mixture to the polymeric material, and then curing the appliedpowder mixture to cause adherence to the surface of the polymericmaterial. Electrostatic charging of the powders prior to application isoptional. Curing may be effected by thermal or radiation means. Powdermixing may be performed prior to application, conveniently in afluidized bed. Mixing may also be performed with use of separateapplication means (conveniently two or more Corona discharge guns thatare so directed toward the surface of the polymeric material) to causemixing of the respective powders prior to application. Again, theresulting cured product contains superabsorbent polymeric powderscontained in a cured resinous coating, which is adhered to the surfaceof the polymeric material. As above, curing will not alter the state ofthe superabsorbent polymeric powder.

[0041] In any event, once the powder particles are adhered to the coatedsurface, curing of the coating is effected to further enhance andstabilize the powder coating. Thermal curing through heating to fromabout 30° to 200° C. for times from about one second to 20 minutesrepresents typical conditions. Thermal curing can be, for example,achieved in electric, gas fired or induction heated ovens, infrared ormicrowave heating. Typically, higher temperatures require shorter curingtimes. Radiation curing can be accomplished by exposure of the coatingto ultraviolet, electron beam radiation, etc. Radiation curing,especially by ultraviolet light, is attractive due to its lowtemperature aspects and consequent lack of potential harm to thepolymeric surface. Typically, the coating can be cured using V or Dlamps with an illumination dosage of 200 to 600 watts per linear inchdischarge. Also a dual cure utilizing thermal and radiation curing iscontemplated. Dual curing can be accomplished step-wise orsimultaneously. In any event, curing is effective to reduce the tendencyof the powder to agglomerate and separate from the coated surface of thepolymeric material and also is effective to reduce the loss of fineparticles.

[0042] Full curing may not be required in that curing to the extent topermit handling and avoid undesirable tackiness is sufficient.

[0043] In general, relatively fine particle size distributions arepreferred to coarse particle size distributions due to larger surfacearea and thus, the ability to increase absorbency within normal productusage times. Such increased absorbency reduces the weight of the finalproduct and thus permits a smaller amount of superabsorbent polymer tobe used. Such fine particle sizes, within normal produce usage times, inaddition to increasing the amount of overall liquid that can be absorbedper unit of superabsorbent polymer, also serve to increase the rate ofliquid absorbance. The relatively coarse particle size distributionbelieved to be used commercially, i.e., having and described in thepreviously-mentioned website of Atofina, an average particle size of 420microns, is suitable to achieve certain of the advantages of theinvention if attached to the cured coating of the invention. Suchcertain advantages of the present invention involve stable adherence ofthe powder to the coated polymeric material, thus minimizing loosepowder and powder agglomeration as well as promoting liquid migrationthroughout the absorbent product. In general, particle size is notessential to attaining such advantage, but as discussed in the nextparagraph, particle size distributions less than the coarse commercialpowder offer additional advantages.

[0044] Smaller particle size distributions can provide other importantadvantages. First of all, size distributions smaller than theabove-discussed coarse size distribution provide increased absorbencyrates and, within normal product usage times, provide greater totalabsorbance. For example, a powder having a large proportion of itsparticles below about 200 microns exhibits markedly improved absorbanceproperties when contrasted to a powder having a coarse particle sizedistribution, such as the above-mentioned Atofina superabsorbent powder.Further benefits may be achieved with particle size distributionswherein a large proportion of the particles are below about 100 micronsor even lower.

[0045] As can be appreciated, the property relationship that smallerparticle size distributions enhance the overall or total amount ofliquid that can be absorbed per unit of weight of superabsorbent polymermay enable the absorbent product manufacturer to utilize a smalleramount or weight of superabsorbent polymers and yet achieve the sameamount of absorbency achieved by larger particles of the same weight.Such advantage results in the ability to produce smaller, less costlyabsorbent products that have the same absorbency as that of more bulkyproducts. Another absorbance property of significance is that thesmaller the particle size distribution, the higher the rate of liquidabsorbance. This property can be utilized advantageously for absorbentproducts where comfort and hygiene are considered to be important, suchas diapers, adult incontinence products, and other absorbent productswhich absorb body fluids, and the like. Obviously, the combination ofimproved rate of absorbance coupled with improved total absorbance wouldespecially contribute to the comfort of the user of diapers and adultcontinence products and be beneficial in the fields of water andnutrient retention and erosion control.

[0046] One criteria for selection of a particle size for commercial useis believed to be one of economics; that is, a balance between the costto achieve a given absorbency benefit vs. the cost savings realized inbeing able to use a lesser amount of superabsorbent polymer. Thus, costconsiderations could result in not using very small sized particles eventhough the above-mentioned absorbency properties and advantages could beobtained thereby. It is also pointed out that smaller particles, ingeneral, are believed to be more adherent to the liquid resin coatingthan more coarse particles. On the other hand, very fine particles, suchas less than 10 microns, could involve handling and processing problems.

[0047] Thermoplastic resinous powders will repeatedly melt whensubjected to heat and solidify when cooled.

[0048] Thermoplastic resinous powders useful in the invention includevinyls, polyolefins, nylons, polyesters, copolymers of ethylene andvinyl alcohol, and like resinous powders. When heated above theirmelting points, thermoplastic resins melt and flow to form a coating.When the resin melts and flows, superabsorbent polymeric powders thatare proximate to the thermoplastic resinous powders become stablyadhered to the coating. Thus, when thermoplastic resinous powders andsuperabsorbent polymeric powders are coated onto a surface of asubstrate, such as a polymeric sheet or fiber, the above-mentionedmelting and flow results in particles of superabsorbent polymericpowders becoming stably adhered to the substrate. When heated above therespective melting points, superabsorbent polymeric powders do not meltand flow and thus remain as discrete particles in the coating.

[0049] Another process comprises providing a thin film (on the order ofabout 0.2 mils to about 10 mils) of a thermoplastic resinous material,with or without openings in such films; applying, by suitable means, asuperabsorbent polymeric powder to the film; and heating the film tocause melting and thereby stably adhering the superabsorbent polymericpowder to the film. Typical contemplated heating temperatures are on theorder of 300° C., higher or lower, depending upon the size of theparticles and transfer time of the heated particles to the surface ofthe film.

[0050] Another process embodiment comprises heating the superabsorbentpolymeric powder to a sufficient temperature to cause stable adhesion ofthe superabsorbent polymeric powder to the thermoplastic film. Asuitable heating temperature will result in softening of thethermoplastic resinous material. Typical contemplated heatingtemperatures are on the order of 200° C., higher or lower, dependingupon the size of the particles and transfer time of the heated particlesto the surface of the film.

[0051] When softening is employed, pressure or impingement of the powderonto the film, may be applied to assist adhesion. A convenient method ofpressure application comprises a roll assembly. The roll may optionallybe heated to further assist adhesion.

[0052] Another embodiment comprises heating the superabsorbent polymericpowder, rather than the film, then applying said heated powder to thefilm to cause melting of the film at the point between the heated powderand the thermoplastic resinous film, thereby stably adhering the powderto the film. Typical contemplated heating temperatures are on the orderof 400° C., higher or lower, depending upon the size of the particlesand transfer time of the heated particles to the surface of the film.

[0053] Another embodiment comprises heating the superabsorbent polymericpowder, rather than the film, then applying said heated powder to thefilm to cause softening of the film at the point between the heatedpowder and the thermoplastic resinous film, thereby stably adhering thepowder to the film. Typical contemplated heating temperatures are on theorder of 300° C., higher or lower, depending upon the size of theparticles and transfer time of the heated particles to the surface ofthe film. Pressure may be subsequently applied to the softened film andsuperabsorbent polymeric powder to further adhere these materials.

[0054] Under either of the above four methods, the film with stablyadhered superabsorbent polymeric powder can be used as a core forabsorbent products, such as diapers. Obviously, multiple cores may beused should expected liquid input exceed the capacity of a single core.

[0055] The melting point of the thermoplastic resin should be lower thanthat of the substrate to avoid impairing the properties of thesubstrate. Melting points on the order of about 250° C. arecontemplated. Melting points on the order of 200° C. and lower arepreferred to avoid such impairment, to reduce processing times, or toreduce energy costs.

[0056] It is also desirable, but not essential, that the thermoplasticresin absorb some quantity of water-containing liquids because both thethermoplastic resin and the superabsorbent polymeric powder can then beused to absorb such liquids. Such dual absorbency permits the use ofreduced quantities of the superabsorbent polymeric powder, resulting inan overall economy.

[0057] For example, a thermoplastic resin that meets both of theabove-described properties is a copolymer of ethylene and vinyl alcohol.Typical copolymers include ethylene generally in amounts from about 30to about 50 mol %. Such copolymers are sold under the trademark EVAL® byEval Company of America, Pasadena, Tex. The various copolymers areavailable in a variety of co-polymerization ratios and thus afford avariety of melting points and water absorbency. The choice of aparticular copolymer is dependent upon desired processing parameters andproduct properties.

[0058] When applied and coated onto a substrate, separately or as amixture, the thermoplastic resinous powder and superabsorbent polymericpowder may be present in a variety of amounts. Typically, the amount ofthermoplastic resinous powder ranges from 5 wt % to about 20 wt % orhigher, balance essentially superabsorbent polymeric powder. Loweramounts of thermoplastic resinous powders are preferred to enhanceoverall absorbency and thus mixtures containing from about 5 wt % toabout 10 wt % thermoplastic resinous powder, balance essentiallysuperabsorbent polymeric powder, are preferred.

[0059] Generally, as the particle size decreases for superabsorbentpolymeric powders, initial absorbency increases. In the context of thisinvention, superabsorbent polymeric powder particle size distributionsof 100%<210 microns are preferred; and particle size distributions of100%<90 microns, are more preferable. Superabsorbent polymeric powderparticle size distributions having 100%>210 microns lead to theformation of undesirable ball-like discrete particles rather than gel-or paste-like absorption products. The particle size of thethermoplastic resinous powder should be on the order of about 100microns, with less than 100 microns preferred for liquid absorbencyproperties. However, when the trade-off between cost of grinding thethermoplastic resinous powder below about 100 microns and theimprovement in absorbency is considered, the particle size becomes amatter of choice.

[0060] A variety of curable resins including epoxies, saturated andunsaturated polyesters, polyester-epoxy hybrids, acrylics, andadmixtures thereof may be utilized in the invention. When heated abovetheir respective curing temperatures or exposed to radiation curing, asthe case may be, curable resins flow to form a coating. When the resincures, superabsorbent polymeric powders that are proximate to thecurable resins become stably adhered to the coating. Thus, when curableresin powders and superabsorbent polymeric powders are coated onto asurface of a substrate, such as polymeric sheets or fibers, theabove-mentioned curing results in particles of superabsorbent polymericpowders becoming stably adhered to the substrate. When curing occurs,the superabsorbent polymeric powders do not cure or melt and thus remainas discrete particles in the coating.

[0061] The curing temperature of the curable resin should be lower thanthat of the substrate to avoid impairing the properties of suchmaterial. Curing temperatures on the order of 400° F. or lower arecontemplated, with curing temperatures on the order of 300° F. or lowerbeing preferred to avoid such impairment, to reduce processing times,and to reduce energy costs.

[0062] Radiation curable resins include unsaturated polyester resinsalong with vinyl ether or an acrylate crosslinker and a photoinitiator.

[0063] Curable resinous powders that cure at temperatures below about300° F. and lower are well established. The above-mentioned epoxy,polyester, polyester-hybrid, acrylic, and admixtures thereof resinsutilize curing agents and/or catalysts capable of obtaining curingtemperatures on the order of 300° F. and less.

[0064] Low-temperature curing epoxy resin systems such as set forth inU.S. Pat. Nos. 5,714,206 and 5,721,052, are suitable for use in thisinvention. Both systems are curable at temperatures of 300° F. or below.

[0065] U.S. Pat. No. 5,270,416 also discloses glycidyl methacrylatecontaining resins crosslinked with carboxylic acid functionalcrosslinkers and polyesters. If acrylic resins are used, GMA resins suchas PD 7690 from Anderson Development Company can be used with DDA ascuring agent in presence of catalysts that promote this reaction.Crosslinkers may comprise aliphatic dicarboxylic acid.

[0066] U.S. Pat. Nos. 4,147,737 and 5,168,110 disclose other glycidylfunctional crosslinkers that can be used with acid functional polyestersas thermosetting powder coating compositions. Epoxy resins such as thatare based on bisphenol A can also be used as crosslinkers to form hybridpowder coatings. Such epoxy resins are disclosed in U.S. Pat. No.5,721,052.

[0067] European Patent Application 0 214 448 (A2) discloses compositionscontaining acid group containing acrylic polymer and epoxy resins.

[0068] Acrylic resins for hybrid coating powders are available from SCJohnson. Product designations include SCX820, 831, and 848.

[0069] In all of the above compositions, suitable catalysts can be usedto enhance low temperature cure characteristics. For all of thethermosetting compositions involving acid functional and glycidylfunctional materials suitable catalysts can be chosen from amines (suchas DBU), ammonium salts (such as tetra butyl ammonium bromide, benzyltrimethyl ammonium chloride), phosphine (such as triphenyl phosphine),phosphonium salts (such as ethyl triphenyl phosphonium bromide),imidazole (such as 2-methyl imidazole, 2-phenyl imidazole), imidazoleadducts (such as P101 from shell, HT 3261 from Ciba Geigy) can be used.U.S. Pat. Nos. 5,169,473 and 4,868,059 disclose catalysts useful forcrosslinking glycidyl containing resins. Examples of catalyst that arediscussed in these patents are compounds containing amine, phosphine,heterocyclic nitrogen, ammonium, phosphonium, arsonium or sulfoniummoieties. Especially preferred are the alkyl-substituted imidazoles;2,5-chloro-4-ethyl imidazole; and phenyl substituted imidazoles, andmixtures thereof. Even more preferred are 2-methyl imidazole; 2-ethyl,4-methyl imidazole; 1,2-dimethylimidazole; and 2-phenyl imidazole.Especially preferred is 2-methyl imidazole. Particularly suitablecatalysts are those quaternary phosphonium and ammonium compounds suchas, for example, ethyltriphenylphosphonium chloride,ethyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide,ethyltriphenylphosphonium acetate, ethyltriphenylphosphonium diacetate(ethyltriphenylphosphonium acetate acetic acid complex),ethyltriphenylphosphonium tetrahaloborate, tetrabutylphosphoniumchloride, tetrabutylphosphonium bromide, tetrabutylphosphonium iodide,tetrabutylphosphonium acetate, tetrabutylphosphonium diacetate(tetrabutylphosphonium acetate acetic acid complex),tetrabutylphosphonium tetrahaloborate, butyltriphenylphosphoniumtetrabromobisphenate, butyltriphenylphosphonium bisphenate,butyltriphenylphosphonium bicarbonate, benzyltrimethylammonium chloride,benzyltrimethylammonium hydroxide, benzyltrimethylammoniumtetrahaloborate, tetramethylammonium hydroxide, tetrabutylammoniumhydroxide, tetrabutylammonium tetrahaloborate, and mixtures thereof andthe like.

[0070] Other suitable catalysts include tertiary amines such as, forexample, triethylamine, tripropylamine, tributylamine,benzyldimethylamine, imidazoles such as 2-methylimidazole mixturesthereof and the like.

[0071] Other suitable catalysts include ammonium compounds such as, forexample, triethylamine.HCl complex, triethylamine.HBr complex,triethylamine.HI complex, triethylamine.tetrahaloboric acid complex,tributylamine.HCl complex, tributylamine.HBr complex, tributylamine.HIcomplex, tributylamine.tetrahaloboric acid complex,N,N′-dimethyl-1,2-diaminoethane.tetrahaloboric acid complex, andmixtures thereof and the like.

[0072] Other suitable catalysts include quaternary and tertiaryammonium, phosphonium, and arsonium adducts or complexes with suitablenon-nucleophilic acids such as, for example, fluoboric, fluoarsenic,fluoantimonic, fluophosphoric, perchloric, perbromic, periodic, mixturesthereof and the like. U.S. Pat. No. 5,169,473 discloses latent catalyststhat are useful for the present invention.

[0073] When applied and coated onto a substrate, separately or in amixture, the ratios of curable resinous powder and superabsorbentpolymeric powder may be present in a variety of amounts. Typically, thecurable resinous powder is present in an amount from about 5 to about20%, balance superabsorbent polymeric powder. It is preferred to utilizefrom about 5 to about 10% curable resinous powder, balancesuperabsorbent polymeric powder, to enhance liquid absorbance.

[0074] The powders and powder mixtures of the invention may be appliedto a substrate with use of conventional means and techniques such asslot coating, Corona discharge guns, tribocharging apparatus, curtaincoating, air-assisted coating techniques, etc.

[0075] Powders suitable for the invention may be made using conventionaltechniques such as extrusion and grinding. Conventional cryogenicgrinding techniques may be desirable when grinding thermoplasticresinous material into powders due to the toughness of such material. Itis also contemplated that superabsorbent polymers may be ground with thethermoplastic resin and the resultant product applied to a substrate inaccordance with the invention. Typically, the respective materials maybe in particulate form prior to grinding to obtain smaller particles.Production of very fine size distributions such as less than 10 microns,and even from 2 to 5 microns, can be manufactured with the use of jetmilling or other technology. Direct particle production such as shown inU.S. Pat. Nos. 5,766,522; 5,708,039; 4,582,731; 4,734,451; 4,012,461;5,027,742; 5,171,613; 4,734,227; 5,997,956; and 6,132,653 can also beused to produce particles for the invention. Said patents areincorporated herein by reference. It is also contemplated that directlyproduced particles or powders can be generated and then immediatelyplaced in contact with the liquid coated polymeric material.

[0076] Above-mentioned U.S. Pat. No. 5,766,522 discloses the use ofsupercritical conditions to produce resinous particles. Carbon dioxidemay be used as a solvent for the process. The Ohio State UniversityCollege of Engineering, in its publication entitled, “News inEngineering,” Vol. 70, No. 2, describes the treatment of polymers undersupercritical conditions to expand polymer fibers to increaseabsorbency. This publication also discloses supercritical carbon dioxidecan carry additives, such as molecules of surfactants or soaps, deepinto materials such as cloth, plastic, and paper. However, there is nomention of carrying superabsorbent particles into such materials.

[0077] The process of the present invention permits incorporation ofsuperabsorbent material (powder or film) into polymeric materials bytreating the polymeric material with a superabsorbent material containedin supercritical fluid solvents, such as carbon dioxide, methanol, etc.Aforementioned U.S. Pat. No. 5,766,522 mentions various other suitablesolvents.

[0078] It is contemplated by the present invention that resinoussuperabsorbent polymer particles or films could be generated in situunder supercritical conditions and then incorporated into a polymer thatis being treated supercritical conditions, such as with supercriticalcarbon dioxide. Alternatively, premanufactured particles could be addedunder supercritical conditions to achieve incorporation. Under eitherprocess, liquid absorbency of the treated polymer would be increased,thereby offering a new class of highly absorbent products.

[0079] The invention may also be advantageously used to enhance theabsorbency of cleaning products designed for wiping or absorbingliquids, particularly aqueous liquids, such as water or water-basedliquids. Such products made according to the present invention exhibitincreased rates of absorbency, especially during initial stages of use.Particle size distribution is important to achieve the rapid aqueousabsorption rates required for wipes. To demonstrate this inventivecharacteristic, the absorbency data set forth below was obtained. Threedifferent 0.1 gram powders, each having different particle sizedistributions, were placed in filter bags made from USA filter paper,which was made from non-chlorinated blended fibers and sold by MiniminitProducts, Ltd., Scarborough, Ontario, Canada, and then immersed in a cupof distilled water for thirty seconds. The superabsorbent particles ofSamples A and B were obtained from Aquatine, Inc., P.O. Box 5168,Lakeland, Fla. 33807, and sold under the name AOG-40 and AOG-44. SampleC was obtained by grinding and screening a portion of Sample B to asmaller size. The following experimental results were obtained and areset forth in the following table. SAP Particle Weight Gain SizeIncluding Appearance of SAP Sample Distribution Filter Bag FollowingImmersion A 100% > 210 2.0 Ball-like discreet (AOG-40) microns particlescontain absorbed water B 100% < 210 18.9 Gel- or paste-like (AOG-44)microns, material containing 35% < 90 absorbed water microns C 100% < 9019.7 Gel- or paste-like (AOG-44, ground microns material containing andscreened) absorbed water

[0080] Based upon the above data, it is clear that the gel- orpaste-like resulting material exhibited much superior absorbance. Hence,a sufficiently small size distribution to achieve such gel-like materialresults in a superior wipe. Clearly, an SAP particle size distributionhaving a large proportion of particles less than 200 microns wouldachieve such gel and accompanying desired result. Sample C is consistentwith the result of Sample B and achieves further superior absorbency.

[0081] As can be appreciated, the powder stably adhered to the curedresin coating should have a particle size distribution sufficient toform a gel upon contact with aqueous solutions. A convenient powderparticle size distribution to form a gel is one having essentially about100% of its particles below about 200 microns and 35% below about 100microns. Finer particle size distributions, such as those having about100% of its particles below about 100 microns, are believed to befurther advantageous.

[0082] It should be understood that a wipe could comprise a polymericmaterial having a cured liquid resin and adhered superabsorbent powderon one or both wipe surfaces. Alternatively, an absorbent core of theabove-coated material could be interposed between two water permeablesheets or between one water impermeable sheet and one water permeablesheet.

[0083] Two different SAP particle size distributions were evaluated tosimulate conditions encountered during the use of a diaper. One-gramsamples of each particle distribution were placed in the same filterpapers described above. Samples and B correspond to Samples A and B ofthe above wiping experiments. The samples were immersed in a containerhaving 0.9% wt % sodium chloride in water for five time intervals. Thissodium chloride-containing solution was provided to simulate urine. thefollowing experimental results were obtained and are set forth in thefollowing table. Weight Gain per one gram of Super SAP Absorbent Polymer(in grams) after specified Particle Size time (in minutes) SampleDistribution ½ min 1 min 5 min 10 min 30 min A 100% > 210 7.1 11.5819.52 27.60 33.85 (AOG-40) microns B 100% < 210 27.59 31.04 34.01 34.3234.36 (AOG-44) microns, 35% < 90 microns

[0084] Based on the previously mentioned Atofina website, a typicaldiaper may contain anywhere about 10 grams to 20 grams of superabsorbentpolymer. Normal diapers typically utilize about 10 grams or less of SAPand thinner diapers, pads, or adult incontinence products, contain from10 to 20 grams of SAP. In general, the thinner the product, the higheramount of SAP that is included. Two diapers are weighed after usage, andthe weight gain is approximately 200 grams. If 10 grams of SAP was used,then the weight gain per gram of SAP is about 20 grams. This indicatesthat normal usage time of a diaper corresponds to 5 and 10 minutes ofthe above experimental times. At 5 and 10 minutes, the difference inweight gain between respective particle sizes is very significant. Theparticles of Sample B can absorb about 75% more at 5 minutes and 25%more at 10 minutes. This indicates that the usage of SAP in diaperproducts may be reduced by at least 25% by weight, and similarperformance with respect to the total absorbency of the diaper can bemaintained. Another benefit is that the faster rate of absorption of thefiner particles will maintain the contact surface drier than coarseparticles.

[0085] The above data also indicate that thin absorbent products, suchas adult incontinence products, can benefit to a greater extentregarding contained SAP weight than normal diapers because of the higheramount of the contained SAP. Another benefit is that such desirably thinproducts can be made even thinner without loss of important absorbencyproperties.

[0086] It is believed that the above Table indicates that finerparticles lead to increased rates of absorbance, at least during initialusage times. Finer particles, at least during normal diaper usage times(prior to saturation) are believed to lead to increased totalabsorbance. Please note that the data following the 30 minutes ofimmersion is believed to reflect product saturation—an event that wouldrarely occur during actual use. It is believed that the data obtainedfollowing up to 10 minutes of immersion is more typical of actual use.

[0087] A general example of a typical combination of process steps thatcan produce the product of the invention is as follows:

[0088] First, a sheet of cellulosic fibers is provided and then is spraycoated with a UV-curable liquid urethane resin. Then such coated fibrousmaterial is contacted with superabsorbent polymeric powders comprised ofsodium salts of polyacrylic acid having a size distribution wherein alarge proportion of the particles are less than about 200 microns andthus is caused to adhere to the liquid resinous coating. Thisintermediate product is then exposed to ultraviolet radiation from Hlamps with less than one second exposure to cure the resin and therebystably affix or stably adhere the powder particles to the surface of thecured resin. The resultant sheet product is no longer tacky followingthe curing step and is then stacked with like sheets to form a liquidabsorbent product or core which is then disposed between a liquidpermeable sheet and a non-liquid permeable sheet to form a diaper.

[0089] Another process embodiment is illustrated below.

[0090] A sheet of cellulosic fibers is provided and then is coated withan aqueous solution containing a polyacrylic acid resin. Followingevaporation of the water at a low temperature such as 100° F., the samepowder described in the example is applied and the process is conductedin the same manner. A resultant product similar to that of the aboveexample is obtained.

[0091] It will be understood that a coil of polymeric material, such ascellulosic material, could be used instead of an individual sheet andthe process conducted in a continuous manner passing the coil webthrough various processing stations. The web can then be recoiled orindividual sheets cut from the coil following the curing step. Alsoindividual sheets can be placed in a moving belt and continuously orsemi-continuously moved from a coating station to a powder applicationstation, to a curing or melting station, and to a stacking station.

[0092] The data contained in the following table illustrates the use ofthermoplastic resinous powders and superabsorbent polymeric powders forabsorbent products. THEO- RETICAL WEIGHT WT TOTAL WEIGHT GAIN BY WT OFOF WT OF WEIGHT GAIN BY SAP and TRIAL COTTON SAP* TRP** GAIN COTTON TRPA 1.4 — — 32.0 — — B 2.0 1.0 — 69.0 45.6 23.4 C 1.4 — 1.0 38.9 31.9 7.0D 1.7 0.9 0.1 65.3 39.0 26.3 E 2.1 0.8 0.2 67.0 47.9 19.0 F 2.7 0.9 0.183.3 61.6 21.7

[0093] The trials were conducted by immersing approximately 3-inchcotton squares containing the ingredient(s) specified in the above tableinto a 0.9 wt % NaCl aqueous solution for one minute. The cotton squareswere separated into two essentially equal layers, the ingredient(s) wereplaced in between such layers, and the layers were lightly pressedtogether. The thermoplastic resinous material selected for the abovetrials is sold under the trademark EVAL® G156B by Eval Company ofAmerica, Pasadena, Tex. This resin is an ethylene vinyl alcoholcopolymer containing 48 mol % ethylene. Following placement into thecotton square and prior to immersion, the samples containing thethermoplastic resinous powder were heated in a 200° C. oven for oneminute. Such temperature and time was sufficient to melt the resin.

[0094] Example A indicates that the cotton fiber used in the trialsabsorbs about 22.8 grams of the aqueous solution per gram of cotton.

[0095] Example B indicates that one gram of fine superabsorbentpolymeric powder (100%<210 microns, 35%<90 microns) absorbs about 23.4grams of the aqueous solution.

[0096] Example C indicates that one gram of a fine thermoplasticresinous powder (<100 microns) absorbs about 7 grams of the aqueoussolution.

[0097] Example D indicates that one gram of a mixture of a 10 wt % offine thermoplastic resinous powder, balance fine superabsorbentpolymeric powder, absorbs about 26.3 grams of the aqueous solution.

[0098] Example E indicates that one gram of a mixture of a 20 wt % offine thermoplastic resinous powder, balance fine superabsorbentpolymeric powder, absorbs about 19.0 grams of the aqueous solution.

[0099] Example F indicates that one gram of a mixture of a 10 wt % ofcoarse thermoplastic resinous powder, balance fine superabsorbentpolymeric powder, absorbs about 21.8 grams of the aqueous solution.

[0100] Based upon the above information and observation the respectiveproducts following immersion, the following conclusions may be reached.

[0101] First, the thermoplastic resinous powder is effective inabsorbing a minor, but significant, amount of the aqueous solution.

[0102] Second, all thermoplastic resinous powder containing samplesexhibited a continuous gel-like appearance. Thus, ball-like productswere prevented.

[0103] Third, lower wt percentages of thermoplastic resinous powder inthe mixtures result in desirable gel-like products and lead to higheramounts of absorption.

[0104] Fourth, finer thermoplastic resinous powder particle sizedistributions should to lead to slightly higher amounts of absorptiondue to a larger surface area per unit of weight. However, coarserthermoplastic resinous powder particle size distributions are lesscostly to produce and could be preferred for cost reasons.

[0105] In summary, it is believed that fine superabsorbent polymericpowder may be adhered to fibrous substrates, such as cotton, withoutappreciable loss in absorbency. Thus, it is believed that the use ofthermoplastic resinous powders to adhere fine superabsorbent polymericpowder to materials in absorbent products permits the improvedabsorbency benefit of the fine superabsorbent polymeric powder to berealized without incurring segregation of the particles in the absorbentproduct.

[0106] As mentioned previously, prior methods of erosion and irrigationcontrol involve incorporating superabsorbent polymeric powder into soilto prevent erosion and water loss or placing elongated elements to forma barrier in soil to prevent erosion. The present invention utilizessuperabsorbent polymeric powder in a distinct, highly advantageousmanner to enhance erosion and irrigation control and to direct thegrowth of plant roots. Such advantages are obtained by stably adheringsuperabsorbent polymeric powder to elements designed to achieve variouspurposes.

[0107] Superabsorbent polymeric powder is stably adhered to waterretention elements rather than being scattered or mixed into the soil.Such elements are stably adhered to superabsorbent polymeric powder,which absorb and store water under the ground. However, it iscontemplated that superabsorbent polymeric powder may be distributed inthe soil in combination with the use of the superabsorbent polymericpowder coated elements of the invention. Placement of these elementsinto the ground creates a stable system for absorbing and storing waterintroduced into the soil. Following storage, the absorbed water is thenadvantageously dispensed back into the ground and/or becomes absorbed byplant roots. The above-described invention avoids situations where thesuperabsorbent polymeric powder become washed away or segregated due towater introduction or other causes.

[0108] The elements may conveniently comprise rigid materials such asplastic, metal, wood, or other materials, or non-rigid woven ornon-woven fibrous materials such as cotton, burlap, wood chips, planthusks, etc. The elements may preferably contain openings to permit thepassage of water and nutrients. Such openings, in combination with thestructure of the element, provide a free volume sufficient to permit thesuperabsorbent polymeric powder to expand upon contact with a liquid.Otherwise, water absorption could be retarded should an inadequate freevolume exists. Honeycombed openings are contemplated as well as othertypes of openings. Suitable element shapes include sheets, cylinders, orother configurations. Cylindrical elements may be formed by wrapping aflat sheet into a cylinder. Multiple wrapped layers are contemplated.All elements may be coated on one or both sides. In the case of hollowor multiply wrapped cylindrical elements, the interior and/or exteriorof such element may be coated; and sufficient free volume is createdthereby. The element may be coated only on specific areas. In such case,an element could be inserted into the ground with only the coated areaabsorbing water. Such procedure would obviously enable water storage tobe obtained at a specific location under the ground and not in anundesired area.

[0109] All of the methods previously described in this application forstably adhering superabsorbent polymeric powder to an element aresuitable for use in preparing water retention elements for irrigation,erosion, and plant root direction usage.

[0110] Generally, copolymers of acrylic acid, acrylamide, and anybi-functional monomer that can provide cross-linking, are suitable forabsorption/retention use. Anionic polyacrylamide polymers are an exampleof a suitable superabsorbent polymeric powder for water retentionpurposes.

[0111] Typical superabsorbent polymeric powder particle sizes for waterretention applications may range from less than about 10 microns toabout 5,000 microns or more. For example, a 500-1,000 micron particlesize is suitable for most applications. Erosion control barrierelements, as well as water or petroleum elements, may benefit fromsmaller particle sizes because smaller particle sizes have the abilityto absorb water and other liquids more quickly than larger particlesizes. The ability to rapidly absorb water is obviously beneficial toerosion control. In addition, rapid absorption of water and petroleum isobviously beneficial for clean-up applications. Particle sizes on theorder of about 10 microns to about 100 microns are especially suitablefor erosion control and clean up.

[0112] Typical amounts of superabsorbent polymeric powder that arescattered or mixed with soil are as follows: 50 gm/m² for grassirrigation; ½ kg/m³ for tree, bush, or plant transplantation; and 100gm/m² for surface application on growing plants. Similar quantities maybe used in the practice of the present invention with exact quantitiesfor all embodiments of the invention being within the skill of the artto determine for specific purposes, materials, climates, and soilconditions with the use of no more than routine experimentation.

[0113] Water retention elements may be generally placed under the groundby forming a hole in the ground, placing the element in the hole, andcovering the hole. Alternatively, if the element has sufficientstructural integrity and the ground is sufficiently soft, the elementmay be placed in a desired location by applying pressure to push theelement into the ground. Such placement also provides aeration of thesoil with accompanying root growth benefits. Mechanical devices may alsobe used to place the element at a desired location. For example, asod-cutting machine could be used to lift sod from a lawn or athleticfield, then a film or sheet-like element placed under the lifted sod,and the sod returned to its original location. If a roll or coil ofelongated, cylindrical element were used, a machine similar to that usedto lay cable in the ground could be employed. Such machine digs atrench, uncoils the cable into the trench, and then covers the trench.It is also contemplated that elements could be placed in the groundduring plowing with use of a coil element that is continuously fed intothe furrow created during plowing.

[0114] Superabsorbent polymeric powder-coated elements may be placed inthe ground to prepare for future usage or placed in the ground after theusage has commenced. For example, a grid of superabsorbent polymericpowder-coated elements may be placed at an underground location an thenan athletic field, golf course fairway or green, lawn, crop, plant, etc.then placed or grown over such grid. Different elements may be placed atdifferent depths in the ground to provide water and nutritionalassistance as growth progresses. Alternatively, the elements can beplaced underground following the commencement of growth on top of theground. The ability to place coated elements in the ground followingestablishment of a plant or crop is important because theabove-described prior art technique of placing absorbent particles belowthe ground would become difficult, if not impossible.

[0115] As mentioned previously, loose absorbent particles have been usedto clean up liquids, including standing water and petroleum spills. Oncethe particle has absorbed the liquid, the particle itself must becollected to complete the clean-up operation. Collection may be atedious process. The present invention provides a solution to theabove-described clean-up problem. The invention may be used to collectstanding water caused by rain from the surface of athletic fields orgolf courses, including greens. The collection or clean up of petroleumspills on land or water is also contemplated. By stably adhering anappropriate absorbent polymer on a clean-up element such as a poroussheet, and then placing such sheet in contact with the liquid, one caneasily absorb the liquid and then remove the sheet, thereby avoiding theneed for tedious particle collection and removal. The previouslymentioned superabsorbent polymeric powders are suitable for water cleanup, and various well-known petroleum absorbent polymeric powders can beused for petroleum clean up. Such polymers include PETRO BOND® sold byNochar and PETROLSORB® sold by Polymers, Inc.

[0116] Examples of irrigation and erosion control systems of the presentinvention are set forth below.

EXAMPLE G

[0117] Erosion control is affected by placing flat, elongated polymericbarrier elements having openings and coated with stably adheredsuperabsorbent polymeric powder into a steep bank where soil erosion isdesired to be prevented. For example, hills, terraces, stream banks, orother areas where erosion is undesirable, could benefit from thisprocedure. The barrier element absorbs water rapidly and then holds suchabsorbed water until a time when the water is gradually released fromthe superabsorbent polymeric powder back into the soil. Such cycle isrepeated as the relative amount of water in the soil changes.

EXAMPLE H

[0118] Example G is repeated except that cylindrical erosion barrierelements are employed. Such barriers are coated on interior surfaceswith superabsorbent polymeric powder. Holes are made in the soil,cylindrical erosion barrier elements are placed in such holes, and thehold is covered with soil to permanently affix the erosion barrier inthe hole.

EXAMPLE I

[0119] Example H is repeated except that the cylindrical erosion barrierelement has a pointed end and is placed into the soil by applyingsufficient pressure to the other end of the cylinder to cause thecylinder to penetrate and become lodged in the soil. Alternatively, theelement is in the form of a spiral and is screwed into a desired site inthe soil.

EXAMPLE J

[0120] A lawn is desired to be irrigated by spraying water on thesurface of the lawn. Prior to irrigation, a flat element coated withstably adhered superabsorbent polymeric powder is placed beneath andparallel to the surface of the lawn. Upon watering the lawn, waterpasses through the surface of the lawn into the underlying soil and isabsorbed and retained by the element. The absorbed water is releasedwhen the soil becomes dry again and is utilized to feed the lawn,thereby reducing the need for future watering.

EXAMPLE K

[0121] Example J is repeated except that in addition to theabove-described placement of the flat element, other elements are placedperpendicular to the surface of the lawn and along the lawn perimeterand retain water that would otherwise escape from the perimeter of thelawn.

EXAMPLE L

[0122] Examples J and K are repeated except that the lawn is located onan athletic field.

EXAMPLE M

[0123] Example J is repeated and the flat element is placed under thelawn by lifting the lawn sod and inserting the flat element thereunder.

EXAMPLE N

[0124] Example J is repeated and the element is cylindrical and isplaced under the lawn by using an apparatus capable of digging a trenchin the lawn, placing the, cylindrical element in such trench, and thenreplacing the sod removed by such digging onto the top of the trench,thereby burying the cylindrical element.

EXAMPLE O

[0125] A nursery desires to grow young trees and then transplant suchtrees to another area for subsequent growth. A common problem with theabove procedure is that the roots from the young trees extend beyond thearea where the root-containing ball of the tree is dug out. The rootsextending beyond the ball area must be severed during removal. Removalof such roots adversely impacts subsequent tree growth. The followingprocedure is used to prevent the above problem. When growth of the youngtrees is initiated, water retention elements are placed in thecontemplated root ball area. Upon watering the trees, the elementsabsorb and retain water, thereby causing the root system of the youngtree to become focused in the area of the elements and extend into anon-desired area located away from the contemplated root ball area to alesser extent than had the elements not been placed as described above.The trees become more mature and are then removed, stored, andtransplanted to a new location.

EXAMPLE P

[0126] A homeowner is experiencing underground sewer clogging and damagebecause of tree roots entering into the sewer seeking water. Waterretention elements are placed at location(s) sufficiently remote fromthe sewer to attract the tree roots, and the sewer is cleaned. Futureclogging and damage to the sewer is minimized thereby.

EXAMPLE Q

[0127] A homeowner is experiencing damage to a driveway because treeroots are causing breakage of the driveway. Water retention elements areplaced at several locations sufficiently remote from the driveway toattract the tree roots, thereby preventing further damage to thedriveway.

EXAMPLE R

[0128] It is desired to grow a tree having a deep root system in an aridarea. Normally, it is very difficult to grow such a tree because wateris not available at a deep location to attract the roots. Consequently,if the tree can be grown at all, a shallow root system will develop; andthe tree will be vulnerable to uprooting due to wind, etc. To preventsuch problem, a water retention element is placed under a deep rootingtree at a location where roots are attracted. Water is absorbed andobtained by the water retention element and becomes dispersed into thesoil as the soil becomes drier. Deep roots are formed.

EXAMPLE S

[0129] It is desired to cause seedling tree roots to grow in a desiredlocation. Prior to planting the seed, water retention elements areplaced in the ground at a location defining the volume of ground thatwill be utilized as a ball for subsequent tree transplantation. A seedis planted in the ground and grows into a seedling tree. The roots ofthe seedling tree are attracted to the water retention elements and aresubstantially directed to the above-mentioned ball location. The tree isremoved along with the ball from the ground and transplanted to anotherlocation.

EXAMPLE T

[0130] Example S is repeated except that the water retention elementsare placed at desired locations after the seedling tree has begun togrow.

EXAMPLE U

[0131] A person desires to go on an extended vacation and is unable tolocate a service to ensure that the potted plants will be watered duringthe vacation. Water retention elements are placed in the soilsurrounding the plant roots. The water retention elements are hollow,cylindrical elements coated on the inside of the cylinder withsuperabsorbent polymeric powder. The hollow nature of the cylinderpermits the requisite free volume. The elements are placed in the soilby applying pressure to one end of the cylinder causing the element toenter the soil and become located at a desired location. A large amountof water is then introduced to the soil. Some of the provided water isutilized by the plant, and other portions of the water are absorbed bythe superabsorbent polymeric powder and thus become stored at a desiredlocation. In the absence of the water retention elements, a largeportion of the provided water would have passed through the soil and outof the pot through a hole at its bottom. While the person is onvacation, the stored water is dispensed from the superabsorbentpolymeric powder into the soil as the soil becomes dry and is utilizedto water the plant roots. Thus, the need for plant watering while theperson is on vacation is eliminated.

EXAMPLE V

[0132] Rain causes standing water to accumulate on a green during a golftournament, thus causing a delay in play after the rain stops. Workersplace a polymeric screen having superabsorbent polymeric powder stablyadhered to the screen into the standing water area of the green. Wateris absorbed by the powder, and water is removed from the surface of thegreen. Multiple placements of additional coated screens are performeduntil a sufficient amount of the standing water has been removed topermit play to continue.

EXAMPLE W

[0133] A petroleum spill occurs on a small body of water. Workers travelto the area of the spill and place a flat clean-up element comprising apolymeric screen stably adhered to a petroleum absorbent polymericpowder into the area of the spill. Petroleum is absorbed by the powder,and the element is removed thereby cleaning up at least a portion of thespilled petroleum.

EXAMPLE X

[0134] Example W is repeated, except that the petroleum spill occurs onland, and the clean-up element is unwrapped from a coil, passedcontinuously through the petroleum spill area, and then recoiled.

We claim:
 1. A water retention element comprising a substrate having asuperabsorbent polymeric powder stably adhered thereto by an at leastpartially melted thermoplastic resin; said substrate having a structurecreating sufficient free volume to permit said superabsorbent polymericpowder to expand upon contact with a liquid.
 2. The element of claim 1,wherein said superabsorbent polymeric powder comprises an anionicpolyacrylamide polymer.
 3. The element of claim 1, wherein saidsubstrate is generally flat.
 4. The element of claim 1, wherein saidsubstrate is generally cylindrical.
 5. A water retention elementcomprising a substrate having openings extending through said substrate;said substrate having a coating stably adhered thereto comprising asuperabsorbent polymeric powder and an at least partially cured resin.6. The element of claim 5, wherein said superabsorbent polymeric powdercomprises an anionic polyacrylamide polymer.
 7. The element of claim 5,wherein said substrate is generally flat.
 8. The element of claim 5,wherein said substrate is generally cylindrical.
 9. The element of claim1, wherein said substrate has openings extended through said substrate.10. A method of improving water utilization efficiency, comprisingplacing a water retention element having superabsorbent polymeric powderstably adhered thereto at a desired location under the ground, saidsubstrate having a structure creating sufficient free volume to permitsaid superabsorbent polymeric powder to expand upon contact with water;contacting said superabsorbent polymeric powder with water to cause saidwater to become absorbed into said superabsorbent polymeric powder,thereby storing said water in said desired location under the ground forfuture dispersion.
 11. The method of claim 10, wherein said elementcomprises a film.
 12. The method of claim 10, wherein said filmcomprises a screen.
 13. The method of claim 10, wherein said elementcomprises a cylinder.
 14. The method of claim 13, wherein said cylindercomprises a wrapped film.
 15. The method of claim 10, wherein placingcomprises forming a hole in the ground, placing said element in saidhole, and covering said hole, thereby locating said element at a desiredlocation under the ground.
 16. The method of claim 10, wherein placingcomprises pushing said element into the ground, thereby locating saidelement at a desired location under the ground.
 17. The method of claim10, wherein said superabsorbent polymeric powder comprises an anionicpolyacrylamide polymer.
 18. The method of claim 10, wherein saidsuperabsorbent polymeric powder has a particle size of about 10 to about5,000 microns.
 19. A method of directing plant root growth, comprisingplacing a root growth directing element having superabsorbent polymericpowder stably adhered thereto at a location under the ground where rootgrowth is desired to be directed, said substrate having a structurecreating sufficient free volume to permit said superabsorbent polymericpowder to expand upon contact with water; contacting said superabsorbentpolymeric powder with water to cause said water to become absorbed intosaid superabsorbent polymeric powder, thereby storing said water in saiddesired location under the ground to cause plant roots to grow towardsaid desired location.
 20. The method of claim 19, wherein said elementcomprises a film.
 21. The method of claim 19, wherein said filmcomprises a screen.
 22. The method of claim 19, wherein said elementcomprises a cylinder.
 23. The method of claim 22, wherein said cylindercomprises a wrapped film.
 24. The method of claim 19, wherein placingcomprises forming a hole in the ground, placing said element in saidhole, and covering said hole, thereby locating said element at a desiredlocation under the ground.
 25. The method of claim 19, wherein placingcomprises pushing said element into the ground, thereby locating saidelement at a desired location under the ground.
 26. The method of claim19, wherein said superabsorbent polymeric powder comprises an anionicpolyacrylamide polymer.
 27. The method of claim 19, wherein saidsuperabsorbent polymeric powder has a particle size of about 10 micronsto about 5,000 microns.
 28. A method of reducing soil erosion,comprising placing an erosion barrier element having superabsorbentpolymeric powder stably adhered thereto at a desired location under theground, said substrate having a structure creating sufficient freevolume to permit said superabsorbent polymeric powder to expand uponcontact with water; contacting said superabsorbent polymeric powder withwater to cause said water to become absorbed into said superabsorbentpolymeric powder, thereby storing said water in said desired locationunder the ground and thereby reducing soil erosion.
 29. The method ofclaim 28, wherein said element comprises a film.
 30. The method of claim28, wherein said film comprises a screen.
 31. The method of claim 28,wherein said element comprises a cylinder.
 32. The method of claim 30,wherein said cylinder comprises a wrapped film.
 33. The method of claim28, wherein placing comprises forming a hole in the ground, placing saidelement in said hole, and covering said hole, thereby locating saidelement at a desired location under the ground.
 34. The method of claim28, wherein placing comprises pushing said element into the ground,thereby locating said element at a desired location under the ground.35. The method of claim 28, wherein said superabsorbent polymeric powdercomprises an anionic polyacrylamide polymer.
 36. The method of claim 28,wherein said superabsorbent polymeric powder has a particle size ofabout 10 microns to about 100 microns.
 37. A method for cleaning upliquids disposed in an area on a surface comprising placing a clean-upelement having an absorbent powder stably adhered thereto in such areato absorb the liquid and then removing the element from the area toresult in the removal of at least a portion of the liquid.
 38. Themethod of claim 37, wherein said absorbent powder comprisessuperabsorbent polymeric powder and said liquid comprises water.
 39. Themethod of claim 37, wherein said absorbent powder comprises a petroleumabsorbent polymeric powder and said liquid comprises petroleum.
 40. Themethod of claim 37, wherein said element is in the form of a coil and isuncoiled, continuously passed through said area, and recoiled.
 41. Themethod of claim 39, wherein said area is on a water surface.
 42. Themethod of claim 39, wherein said area is on a land surface.
 43. Themethod of claim 37, wherein said superabsorbent polymeric powder has aparticle size of about 10 microns to about 100 microns.
 44. A processfor stably adhering a superabsorbent polymeric powder onto athermoplastic resinous substrate comprising: (a) Providing a thin filmof a thermoplastic resin; (b) Applying a superabsorbent polymeric powderonto the surface of said film; and (c) Heating said film andsuperabsorbent polymeric powder to cause said film to melt and saidsuperabsorbent polymeric powder to become stably adhered to said film.45. The process of claim 44, wherein said thermoplastic resinous film isa member selected from the group consisting of vinyls, polyolefins,nylons, polyesters, and copolymers of ethylene and vinyl alcohol, andadmixtures thereof.
 46. The process of claim 45, wherein saidthermoplastic resinous film comprises a copolymer of ethylene and vinylalcohol.
 47. A process for stably adhering a superabsorbent polymericpowder onto a thermoplastic resinous substrate comprising: (a) Providinga thin film of a thermoplastic resin; (b) Applying a superabsorbentpolymeric powder onto the surface of said film; and (c) Heating saidfilm and superabsorbent polymeric powder to cause said film to softenand said superabsorbent polymeric powder to become stably adhered tosaid film.
 48. The process of claim 47, wherein said thermoplasticresinous film is a member selected from the group consisting of vinyls,polyolefins, nylons, polyesters, and copolymers of ethylene and vinylalcohol, and admixtures thereof.
 49. The process of claim 48, whereinsaid thermoplastic resinous film comprises a copolymer of ethylene andvinyl alcohol.
 50. The process of claim 47, further comprising applyingpressure to said film and applied superabsorbent polymeric powder tofurther enhance adhesion.
 51. The process of claim 50, wherein saidpressure is applied by a roll.
 52. A process for stably adhering asuperabsorbent polymeric powder onto a thermoplastic resinous substratecomprising: a) Providing a thin film of a thermoplastic resin; b)Heating said superabsorbent polymeric powder; and c) Applying saidheated powder to said film to cause melting of said film at a point ofcontact between said powder and said film, thereby stably adhering saidpowder to said film.
 53. The process of claim 52, wherein saidthermoplastic resinous film is a member selected from the groupconsisting of vinyls, polyolefins, nylons, polyesters, and copolymers ofethylene and vinyl alcohol, and admixtures thereof.
 54. The process ofclaim 53, wherein said thermoplastic resinous film comprises a copolymerof ethylene and vinyl alcohol.
 55. A process for stably adhering asuperabsorbent polymeric powder onto a thermoplastic resinous substratecomprising: a) Providing a thin film of a thermoplastic resin; b)Heating said superabsorbent polymeric powder; and c) Applying saidheated powder to said film to cause softening of said film at a point ofcontact between said powder and said film, thereby stably adhering saidpowder to said film.
 56. The process of claim 55, wherein saidthermoplastic resinous film is a member selected from the groupconsisting of vinyls, polyolefins, nylons, polyesters, and copolymers ofethylene and vinyl alcohol, and admixtures thereof.
 57. The process ofclaim 56, wherein said thermoplastic resinous film comprises a copolymerof ethylene and vinyl alcohol.
 58. The process of claim 55, furthercomprising applying pressure to said film and applied superabsorbentpolymeric powder to further enhance adhesion.
 59. The process of claim58, wherein said pressure is applied by a roll.